Biogeochemistry and paleoclimate variability during the Holocene: a record from Mansar Lake,Lesser Himalaya

Investigation of biogeochemistry and amino acids on a 30-m-long core from Mansar Lake has thrown light on palaeoclimate variability during the Holocene period. The C/N ratio between 6 and 10 with some deviations and δ13C mostly between −20 and −22‰ in the shallow core, as well as a C/N ratio greater than 13 reaching from 19 to 20 and correspondingly lower δ13C of –28‰ in the deeper core suggest an aquatic source of carbon in the former and a cellulose-rich land plant source in the latter. This is supported by the abrupt increase in organic carbon content in the deeper core compared to the shallow core, which indicates a hot and wet climatic regime during the early Holocene and dry and cold during the late Holocene period. The amino acid data AA-C/C% and AA-N/N% are higher in shallow sediments compared to deeper sediments, indicating an aquatic plant source in the shallow core and greater supply of land plant sources in the deeper core. The lower percentage of the non-protein amino acids β-alanine (ALA) and γ-amino-butyric acid in the shallow core compared to the deeper core indicates different sources of organic matter in the lake basin. The higher amino acid ratio Asp/β-Ala (16.99 av.) and Glu/γ-Aba (18.18 av.) in the shallow core and lower ratios (10.32 and 12.41 av.) in the deeper core, and Asp/Glu (1.52 av.) and β-Ala/γ-Aba (1.61 av.) ratios in the former, which are potential indicators of the nature of the organic matter, are higher in the shallow core relative to the deeper core (1.33 and 1.23 av.), indicating relative biodegradation of organic matter in deeper sediments. It has been observed that the organic matter associated with the dry season is relatively less biodegraded, as evidenced from their higher ratios, and is more biodegraded in the wet season as their ratios are lower in the river sediments. In the absence of a bacterial contribution of organic matter from the soil source in this lake, since Mansar Lake is a non-drainage type, it is envisaged that the climatic variation may be responsible for biodegradation in the deeper core sediments. Therefore, the C/N ratio and δ13C values supported by amino acid data, the latter being significant in revealing primary productivity and a terrestrial source of organic matter, suggest a hot and wet climatic regime during the early Holocene (ca. 7580 bp) and a dry and cold in the late Holocene period (ca. 4050 bp).     

Bimodal stable isotope signatures of Zildat Ophiolitic Mélange, Indus Suture Zone, Himalaya: implications for emplacement of an ophiolitic mélange in a convergent setup

Zildat Ophiolitic Mélange (ZOM) of the Indus Suture Zone, Himalaya, represents tectonic blocks of the fragmented oceanic metasediments and ophiolite remnants. The ZOM is sandwiched between the Zildat fault adjacent to a gneissic dome known as Tso Morari Crystalline (TMC) and thin sliver of an ophiolite called as the Nidar Ophiolitic Complex. The ZOM contain chaotic low-density lithologies of metamorphosed oceanic sediments and hydrated mantle rocks, in which carbonates are present as mega-clasts ranging from 100 meters to few centimeters in size. In this work, calcite microstructures, fluid inclusion petrography and stable isotope analyses of carbonates were carried out to envisage the emplacement history of the ZOM. Calcite microstructure varies with decreasing temperature and increasing intensity of deformation. Intense shearing is seen at the marginal part of the mélange near Zildat fault. These observations are consistent with the mélange as a tectonically dismembered block, formed at a plate boundary in convergent setup. The δ¹⁸O and δ¹³C isotope values of carbonates show bimodal nature from deeper (interior) to the shallower (marginal, near the Zildat fault) part of the mélange. Carbonate blocks from deeper part of the mélange reflect marine isotopic signature with limited fluid–rock interaction, which later on provide a mixing zone of oceanic metasediments and/or hydrated ultramafic rocks. Carbonates at shallower depths of the mélange show dominance of syn-deformation hydrous fluids, and this has later been modified by metamorphism of the adjacent TMC gneisses. Above observations reveal that the mélange was emplaced over the subducting Indian plate and later on synchronously deformed with the TMC gneissic dome.     

Solid waste management through multi-criteria decision making: using analytic hierarchy process as an assessment framework for the Hooghly district,West Bengal

Solid waste management (SWM) is a crucial service governed by urban local bodies (ULB). Hence, it is essential to identify challenges and opportunities in the SWM procedures and practices towards improved delivery of services. In this study, analytic hierarchy process (AHP) has been applied in the three sub-divisional towns of the Hooghly district, West Bengal (India), namely Chandannagar, Hooghly-Chinsurah and Serampore to analyze the existing SWM scenario. As AHP is a Multi-Criteria Decision Making tool, hence, it has been deployed by experts to come up with SWM performance index, clearly demonstrating the strengths and weaknesses of management strategies in selected study sites. This article further advances the significance of the AHP method by carving out multi-layered realities through the quantification of qualitative insights across various segments of waste management in the three towns. While interviews with waste management officials led to the formulation of key performance indicators and sub-indicators matrix, the obtained normalized weights brought to the fore the real engagement and actions executed by each of these towns in managing solid wastes. The application of this innovative AHP method ensured accuracy in the ranking system across performance of the specified ULBs. This AHP-induced situational analysis of SWM is not only significant in terms of policy formulation in the ULBs of the Hooghly district but has potentials to work at scales.

Graphical abstract